drm/amd/display: Add null checks

Added NULL checks before two problematic statements
Signed-off-by: Wang <anguwang@amd.com>
Reviewed-by: Martin Leung <Martin.Leung@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/core/dc_stream.c

@@ -221,6 +221,9 @@ struct dc_stream_status *dc_stream_get_status_from_state(
 {
 	uint8_t i;
 
+	if (state == NULL)
+		return NULL;
+
 	for (i = 0; i < state->stream_count; i++) {
 		if (stream == state->streams[i])
 			return &state->stream_status[i];